The present invention relates to a hot-runner tool with at least one hot-runner section for supplying molten plastic to a injection mold, preferably a multiple injection mold with a pin-point gate for each casting, whereby the hot-runner section has an outer housing with a flow channel, at least one inlet, and at least one outlet and a heat conductor that can be connected to an electric voltage and that the molten plastic flows around.
A hot-runner tool of this type is known from German OS No. 2 938 832. The flow channel in the hot-runner section is demarcated externally by the inner surfaces of the outer housing and internally by a heat conductor. Since the molten plastic flowing into the flow channel is heated from the central heat conductor, it is especially the zone in the vicinity of the conductor that is heated most intensively. A layer of solidified plastic builds up on the inner surface of the outer housing, forming a layer of heat insulation and preventing the heat from flowing through the housing.
Since the molten plastic inside the flow channel partly or completely solidifies there during downtimes, the heat conductor must re-heat the total volume of plastic when operation is resumed. The plastic, however, is a poor heat conductor. An annular molten zone forms in the vicinity of the heat conductor and its thickness depends on the amount of electric power supplied to the conductor. Since the layers of plastic that are farther away from the heat conductor take a long time to heat up, heating times are long.